This invention relates to drive unit assembly, and more particularly to a drive unit assembly for a mass transit vehicle, which provides a significantly lower floor profile.
Mass transit vehicles, such as trolley cars, buses, and the like typically have seats aligned at the lateral sides of the vehicle, with a central aisle and floor extending along the vehicle. In order to facilitate entering and exiting from the vehicle, it is desirable to have the vehicle floor and aisle positioned relatively low to the ground. This provides faster cycle time during stops and facilitates boarding for all passengers, especially for elderly and disabled passengers as well as for children.
Mass transit vehicles typically have several axles that support, drive and steer the vehicle. Many such vehicles provide a rigid axle having an input positioned off-center near one wheel end to form an inverted portal axle configuration. Disadvantageously, this arrangement necessarily eliminates the ride benefits of independent suspension systems.
Another disadvantage with this type of axle is that the low floor profile is limited by the portal axle housing. The system uses an axle shaft assembly that extends underneath the vehicle from the input to the opposite wheel. The input is a differential with a gearset coupled to the axle shaft assembly to drive the wheel ends. The axle assembly includes a short shaft member coupled to drive the wheel end that receives the input directly and a long shaft member coupled to drive the opposite wheel end. The differential and axle shaft assembly are enclosed within an axle housing that extends underneath the floor of the vehicle. Currently, the height between the vehicle floor and ground level is not low enough due to the required suspension clearance between the vehicle floor and the axle housing and bowl for the differential.
Accordingly, it is desirable to provide a drive unit assembly with a single input for driving opposing wheel ends that provides an improved low floor profile to facilitate access to the vehicle.
A vehicle drive unit assembly utilizes a single input to drive opposing wheel ends. Each wheel end is suspended independently and the need for an axle housing is eliminated by externally mounting an axle shaft assembly to interconnect the wheel ends. The input is operatively coupled to only one of the wheel ends and the axle shaft assembly includes multiple shaft members that interconnect the input to the other wheel end. One of the axle shaft members is mounted to a vehicle floor with a bearing mount and includes connection joints at either end to accommodate the independent motion of each wheel end. The floor and the shaft member move together during suspension travel, allowing the floor to have a lower profile then is traditionally available.
In the preferred embodiment, the wheel end assemblies include first and second wheel hubs, respectively, that define respective axes of rotation that move vertically independently from each other. Also, the axle shaft assembly is preferably comprised of at least three (3) axle shaft members. A first axle shaft member is mounted to the vehicle floor, a second axle shaft member is used to interconnect one wheel end assembly to the first axle shaft member, and a third axle shaft member is used to interconnect the other wheel end assembly to the first axle shaft member. The first axle shaft member defines a first shaft axis that is parallel to the axes of rotation for the wheel hubs and the second and third axle shaft members define second and third shaft axes that are transverse to the first shaft axis. Constant velocity joints are mounted at each end of each of the three shafts to accommodate the independent motion of each wheel end.